Since the discovery of quasars in 1960s [1]}, more and more quasars have
been found in the last four decades. More than 120,000 quasars have
been discovered from the recent large
optical spectroscopic surveys, such as the Two-Degree Fields(2dF) survey [2]}
and the Sloan Digital Sky Survey (SDSS)[3]}, [4]}.
Quasar candidates in these surveys were mainly selected by
optical colors. Because of the strong UV and optical emission,
quasars can be usually distinguished from
the stellar objects in the color-color and color-magnitude diagrams based on optical
photometry [5]}, [6]}, [7]}.
However, quasar selections based on the SDSS optical photometry alone become very inefficient
for identifying \(\rm 2.2<z<3.0\)  quasars since they have optical
colors similar to those of normal stars [8]}, [6]}, [10]}, [11]}.
In order to get a more complete sample of quasars, we have to think about other ways to find these SDSS missing
quasars in the 'redshift desert' (\(\rm 2.2<z<3.0\) ).
